Chapter 10 Flashcards
what is photosynthesis?
photosynthesis is the process that converts solar energy into chemical energy
what are autotrophs?
autotrophs sustain themselves without eating anything derived from other organisms, able to produce organic molecules from CO2
Who are photoautotraphs?
Almost all plants, because they use the energy of the sun to make organic molecules
Where does photosynthesis occur?
in plants, algae, certain unicellular eukaryotes, and prokaryotes
What are heterotrophs?
heterotrophs obtain their organic material from other organisms, they consume, humans depend on photoautotrophs for food and oxygen
What are the major locations of photosynthesis?
leaves, chloroplasts are found mainly in cells of mesophyll (interior tissue of the leaf)
How many chloroplasts does each mesophyll cell have?
30-40 chloroplasts
What is stomata?
Microscopic pores on the leaf where CO2 enters and O2 exits
What is chlorophyll?
The pigment that gives leaves their green color and resides in the thylakoid membranes
What does photosynthesis produce?
CO2 is consumed and converted to sugar and oxygen
How do chloroplasts split water?
chloroplasts split water into hydrogen and oxygen: incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product
What type of process is photosynthesis?
Photosynthesis is a redox process
What is oxidized and what is reduced in photosynthesis?
Water is oxidized and CO2 is reduced
Use thermodynamic terms to describe photosynthesis
Photosynthesis absorbs energy making it nonspontaneous, meaning it is endergonic, has a positive delta G, and is anabolic
What does photosynthesis consist of?
consists of the light reactions (photo part) and Calvin cycle (synthesis part)
what does the light reactions do in the thylakoids?
splits h20 to produce O2, reduce electron acceptor NADP+ to NADPH, and generates ATP from ADP by photophosphorylation
what is the source of oxygen in photosynthesis?
WATER
What does the Calvin Cycle (in the stroma) form?
it forms sugar from CO2, using ATP and NADPH
What does the Calvin cycle begin with?
Carbon fixation: incorporating CO2 into organic molecules
what are light dependent reactions?
they use light energy to make two molecules needed for the next stage of photosynthesis : energy storage molecule (ATP) and reduced electron carrier (NADPH)
products of light dependent reactions used in Calvin cycle are** slide 19
ATP and NADPH, and O2
what is wavelength?
wavelength is the distance between crests of waves
what does wavelength determine?
wavelength determines the type of electromagnetic energy
what does visible light consist of?
visible light consists of wavelengths that produce colors we can see
what are pigments? what is the relationship to wavelengths?
pigments are substances that absorb visible light, and different pigments absorb different wavelengths
what do wavelengths do if they are not absorbed or reflected?
they are transmitted
why do leaves appear green?
because chlorophyll reflects and transmits green light
what does light go through in a chloroplast?
light goes through the granum to produce transmitted light
what is an absorption spectrum?
an absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength
what does absorption spectrum of chlorphyll a suggest?
suggests that violet-blue and red light work best for photosynthesis
what is an action spectrum?
an action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process
what happened to areas receiving wavelengths favorable to photosynthesis in Theodor W. experiment?
areas receiving wavelengths favorable to photosynthesis produced excess O2
how was the excess O2 measured in Theodor experiment?
the growth of aerobic bacteria clustered along the alga was a measure of the O2 production
What is chlorophyll A?
the main photosynthetic pigment
What is chlorophyll B?
an accessory pigment, such as chlorophyll B and carotenoids, broaden the spectrum used for photosynthesis
What is the difference in the absorption spectrum between chlorophyll A and B?
the difference in the absorption spectrum is due to a slight structural difference between the pigment molecules
What do carotenoids also function in?
Carotenoids also function in photoprotection; they absorb excessive light that would damage chlorophyll
What happens when a pigment absorbs light?
It goes from a ground state to an excited state making it unstable
What happens when excited electrons fall back to the ground state?
when excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence
what happens if an isolated solution of chlorophyll is illuminated?
it will fluoresce, give off light and heat
what does a photosystem consist of?
a photosystem consists of a reaction-center complex (protein complex), surrounded by light-harvesting complexes
what is a light-harvesting complex?
light-harvesting complexes (pigment molecules bound to proteins) transfer energy of photons to the reaction center
what does a primary electron acceptor do?
in the reaction center, it accepts excited electrons and is reduced as a result
what are the two types of photosystems in the thylakoid membrane?
photosystem II (PS II) functions first and is best at absorbing wavelength of 680 nm
photosystem I (PS I) is best at absorbing wavelength of 700 nm
what is the reaction-center chlorophyll a of PS II called?
if it is a PS II, is called P680
what is the reaction-center chlorophyll a of PS I called?
if it is PS I, it is called P700
What are the two possible routes for electron flow during light reactions?
cyclic and linear
what is linear electron flow?
linear electron flow, the primary pathway, involves photosystems and produces ATP and NADPH using light energy
what is cyclic electron flow?
In cyclic electron flow, electrons cycle back from Fd to PS I reaction center
what are light dependent reactions?
linear electron flow and photo part of photosynthesis
products of light dependent reactions
ATP and NADPH
what does cyclic electron flow use and produce?
cyclic electron flow uses only photosystem 1 and produces ATP, does not produce NADPH or oxygen
what do chloroplasts and mitochondria have in common?
they generate ATP by chemiosmosis, but use different sources of energy
how do mitochondria produce ATP?
they transfer chemical energy from food to ATP
how do chloroplasts produce ATP?
they transform light energy into the chemical energy of ATP
what is chemiosmosis?
the process of moving ions (ex: protons H+) to the other side of the membrane, creating an electrochemical gradient (can be used to drive ATP synthesis)
what happens in mitochondria?
protons are pumped to intermembrane space and drive ATP syntehsis as they diffuse back into the mitochondrial matrix
what happens in chloroplasts?
protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma?
what happens in chloroplasts?
protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma?
what do light reactions do in summary?
they generate ATP and increase the potential energy of electrons by moving them from H20 to NADPH
what does the calvin cycle do?
uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
How does calvin cycle work?
it regenerates its starting material after molecules leave and enter the cycle, it builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH
what power do electrons carried by NADPH have?
they have a reducing power if they are carried by NADPH
what are the 3 phases of the calvin cycle
- Carbon fixation (catalyzed by rubisco) 2. Reduction 3. Regeneration of the CO2 acceptor (RuBP)
What happens to carbon in the calvin cycle?
it enters as CO2 and leaves as a sugar called (G3P)
what must occur for net synthesis of 1 G3P?
for net synthesis of 1 G3P, the cycle must take place 3 times, fixing 3 molecules of CO2
What do plants do on hot, dry days?
They close their stomata, which conserves water but limits photosynthesis, reducing access to CO2 and causing O2 to build up; photorespiration
how can photorespiration be damaging?
it can drain the carbon fixed by the Calvin cycle
What happens in C3 plants in photorespiration?
C3 photorespiration: rubisco adds O2 instead of CO2 in the Calvin cycle, producing a 2 carbon compound
Normally, forms a 3 carbon compound
What happens in photorespiration?
photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar
C4 plants:
C4 plants minimize the cost of photorespiration by incoroporating CO2 into four carbon-compounds
What are the types of cells in C4 plants?
Bundle-sheath cells: arranged in tightly packed sheaths around the veins of the leaf
Mesophyll cells: loosely packed between the bundle sheath and leaf surface
3 step process of sugar production in C4 plants
- production of 4 carbon precursors is catalyzed by enzyme PEP carboxylase in mesophyll cells: PEP carboxylase has higher affinity for CO2 than rubisco, can fix CO2 when CO2 concentrations are low
- 4 carbon compounds exported to bundle sheaths
- Within bundle sheaths, they release CO2 that is used in Calvin cycle
CAM plants
include succulents, use crassulacean acid metabolism to fix carbon
how do CAM plants work?
CAM plants, open their stomata at night, incorporating CO2 into organic acids, stomata is closed during the day and CO2 is released from organic acids and used in Calvin cycle
Summary light reactions:
- are carried out by molecules in the thylakoid membranes
- convert light energy to the chemical energy of ATP and NADPH
- split h2o and release o2 to the atmosphere
